This invention relates generally to belt conveyors and particularly to heavy duty mining and industrial type conveyors characterized by a very long conveying run extending in a single reach with one or more frictionally engaged auxiliary booster drive belts augmenting the head end conveyor drive.
Belt type conveyors are widely used for example in moving coal and ore, both underground from the face to a cleaning and sizing operation, and aboveground from the mine to a loading point. Even in underground applications, some of these are miles long.
There are three general types of these long belt conveyors: 1. cascade; 2. cable belt; and 3. booster type belt.
Cascade conveyors are a series of individual, separately powered conveyors arranged in "cascade" relationship, with one discharging onto another. Although extensively used in the past for conveyors longer than were practical for a single length of conveyor belt, they have several drawbacks including degradation of conveyed material and dust generation at each transfer point, and, when used underground, they require extra brushing to remove overhead rock at transfer points.
Cable belt conveyors have a belt supported between a pair of moving steel cables. Although adaptable to very long lengths of many miles, they are complex, expensive, not easily extended, and require substantial head room limiting their use underground.
Booster type belt conveyors are relatively new, the first believed developed for heavy duty use in a British coal mine about 1976 by Hu Wood, Limited. It was originated as a means of uprating an existing half-mile-long conveyor, but did not address problems of applying the booster concept from the outset as a means of providing a long distance transport system which could be extended to a length of several miles as needed.
The booster type belt conveyor offers economic and operational advantages for materials handling over long distances both underground and aboveground. It comprises a conveyor belt having conveyor and return runs trained for orbital movement between driving and idler pulleys located respectively at head and tail ends. One or more intermediate booster belts are trained for orbital movement between driving and idler pulleys with their driving runs in frictional driving engagement with the upper, carrying run of the conveyor belt. Drive motors are connected to the driving pulleys.
In a typical coal mining operation, a booster type belt conveyor may initially be a few hundred or a few thousand feet long. As it is extended, for example, to follow an advancing mine face, it may become several miles long with booster drive belts spaced apart at intervals of a mile or so. Starting such a long conveyor involves many problems. The motor or motors in each driving unit will often require hundreds of horsepower and the booster driving units will be located beyond the sight and hearing of the operator at the main control station. Because the motors take six or more times full load current to start from rest, the power to start all the motors at once could place an unacceptable load on an electrical power source.
Sequential starting is therefore essential. This however can introduce localized stretching of the conveyor belt at the driving point, and severe stress differentials on opposite sides of the drive pulley. This can produce an undesirable "ripple" or wave effect moving along the conveyor as one driving unit after another is powered, and require special, costly, high tensile strength belting, and complex, costly, takeup loop structures for absorbing surplus or stretched belting.